Optical control of molecular high spin states via spin-forbidden transitions

Abstract

We show TDESR to measure the high frequency electron spin resonance spectra of the molecular nanomagnet Fe3CrSMe. We demonstrate the use of a mechanically-detected EPR setup with optical excitations and tunable frequency sources to induce magnetic resonance transitions which are detected using cantilever torque magnetometry. Furthermore we show how we combined TDESR with Photon excited Torque Magnetometry (PheToM) to excite and detect a spin forbidden transition (S=6 to S=7) in Fe3CrSMe. The results are compared to simulations and AC-SQUID results. The use of spin-forbidden transitions is particularly tempting, as it allows connecting otherwise separated Hilbert spaces. This enables to operate qubits in an excited state, without disrupting their ground state coherences. Such spin-forbidden manipulation scheme had been proposed nearly thirty years ago by the pioneer of molecular magnetism O. Kahn, but has remained unobserved due to the considerable experimental diffculties involved.